Mt. Merapi located in the Central Java-Indonesia is the most active volcano over the world. The disaster usually occurs when the hot pyroclastic flows reached to the dense populated area around the volcano. The latest eruption in November 2010 caused fatalities to about 150 people died and 280.000 people sent to flee. The pyroclastic flow deposits reached about 15 km from the summit to the southern flank and devastated everything on their path. The eruption also caused significant change to the land cover around the volcano. This paper presents the effect of the hot pyroclastic flows and ashes to the soil layer condition soon after eruption. The purpose of this study is to quantify the damage level of the soil layer in accordance with soil moisture condition. The two scenes of Phased Array L-band type Synthetic Aperture Radar (PALSAR) onboard Advanced Land Observing Satellite (ALOS) were used in this study. The advantage of ALOS/PALSAR is that the sensor can penetrate vegetation canopy. Therefore, the soil layer could be identified clearly. The acquisition dates of the both data are before and after the eruption. Change detection analyses are applied to the two backscatter intensities of ALOS/PALSAR data. The hot pyroclastic flows decreased the backscatter intensity of soil layer about -15 dB. On the contrary, the ashes increased the backscatter intensity of soil layer about 12 dB. The damage levels are calculated by taking the cosine angle of the square root of the two backscatter intensities. The highest damage level was located at the main path of pyroclastic flow deposits. The medium damage level was located at the ashes deposits. The both damage levels might to be caused by the change of soil moisture and texture. This result could be used for delineating farming possibility area and/or disaster recovery after the eruption.

Fig. 1. Color composite of backscattering intensity image of ALOS/PALSAR before and after eruptions.

Fig. 2. The histogram of pyroclastic flows and ashes in β image of after eruption.

Fig. 3. The damage level map of soil layer calculated from the cosine angle of the ratio of the two β data.

Source:

Saepuloh A., Wijaya K., Sumintadireja P., Detecting soil layer condition soon after Merapi eruption 2010 using ALOS/PALSAR data, Proceeding of the Annual Meeting of Science and Technology Studies 2011 (AMSTECS-2011), Tokyo, Japan, in PDF format, ISSN: 2088-2041, pp. 13-16, June 2011.